The literal translation of tu m'étonnes is "you surprise me," but it's often used as a set phrase meaning "you're not kidding," "no kidding," or "tell me something I don't know." Used in this way, it has the opposite meaning of its literal translation—the person is not surprised by what they just heard. Tu m'étonnes is very similar to the English expression "surprise, surprise," which is also used ironically to convey a lack of surprise.

Sans blague is another phrase meaning "no kidding" or, more literally, "no joke." This one, however, can express surprise:

Je suis né le 3 novembre. -Sans blague! Moi aussi! I was born on November 3. -No kidding! So was I!

The verb étonner has the same root as the English verb "to stun." It means "to surprise," "astonish," or "amaze":